One method for identifying particles in a fluid such as water, is to interrogate each of many particle and produce an interrogation pattern representing characteristics unique to each particle. One example is where a system directs a laser beam through water, and a group of photodetectors detect light scattering by particles passing through a small detect zone lying along the laser beam. The outputs of the photodetectors constitute an interrogation pattern. The interrogation pattern is compared to interrogation patterns of each of a group of known species of particles. If there is a high correlation between the unknown particle interrogation pattern and the patterns of a particular known species, then the unknown particle is deemed likely to be of that species. The interrogations and comparisons are carried out by field units that may continuously sample the water at each of numerous water purification plants.
Occasionally, a new species of particle, such as a new species of pathogenic microorganism, becomes of interest. It is possible to occasionally load interrogation patterns of all species of interest onto a computer disc, carry it to each of the field units, and substitute the new group of patterns for those presently in each field unit memory. However, this would result in considerable delay while a technician visits each of the field units and downloads a new disc into them. This also has the disadvantage that it requires considerable labor of personnel to visit each of the field units, and can result in considerable delay before a new dangerous microorganism begins to be detected.
Sometimes, a new organism is introduced into a water purification plant, as by a change in weather or other conditions resulting in a rapid increase in a particular microorganism. It is desirable that persons in charge of the purification or treatment plants learn about this as soon as possible. It would be desirable if the field units could identify the proliferation of a new species (or a great increase in a species that previously occurred rarely) of microscopic particle and quickly notify the central station.